Connectors for high voltage cables used in aircraft ignition systems are subject to extreme operating conditions. The reduced atmospheric pressure in which the connectors are used increases the tendency for flashover or short-circuiting to occur between the igniter and the connector.
In one type of igniter commonly used for aviation engines, a center electrode terminal is recessed within the bore of a tubular ceramic insulator. An outer metallic igniter shell or a tubular metal sleeve attached to the shell surrounds and shields the outside of the tubular insulator. The free end of the sleeve adjacent to an open end of the insulator has an external thread for retaining a coupling nut on a cable connector. When the cable connector is attached to the igniter, an insulator on the connector projects into the tubular igniter insulator bore and a high voltage contact mounted at the end of the connector insulator is urged by springs inside the connector against the center electrode terminal. The cable connector functions both to electrically connect the high voltage cable to the igniter and to prevent flashover or arcing from the junction between the connector contact and the center electrode terminal to the grounded outer shell or sleeve on the igniter.
In the prior art, it is known to provide a resilient rubber grommet or seal between the cable connector and the end of the igniter insulator. Often a spring is arranged to urge the grommet against the insulator end to maintain a tight seal. The function of the grommet is to prevent dirt and moisture from entering an annular space between the insulator on the end of the connector and the tubular igniter insulator. However, sufficient dirt and/or moisture sometimes enters the space between the igniter and connector insulators to cause flashover.